A gas mixture of a CO.sub.2 Transverse Electric Atmospheric (TEA) laser typically comprises a mixture of CO.sub.2 /He/N.sub.2. As a result an optical pulse output includes a desired large main pulse and an undesirable parasitic tail pulse which follows the main pulse. The optical energy of the main pulse primarily results from CO.sub.2 -electron collisions while the energy of the parasitic tail pulse results from excited nitrogen molecules which repump the CO.sub.2 molecules in the ground state. The He gas functions as an inert carrier and as such does not contribute in any appreciable manner to the optical energy output. The N.sub.2 gas functions as a preionization, or pulse conditioning, means by providing ultraviolet (UV) radiation to CO.sub.2 molecules within an electrical discharge region located between a pair of high voltage electrodes.
In order to function as a source of UV radiation the N.sub.2 gas is typically excited by a spark gap, semiconductor preionizer or some other suitable means. The N.sub.2 photoionizes the CO.sub.2 gas by supplying UV photons which are absorbed by the CO.sub.2. The CO.sub.2 thereafter emits electrons, thereby ionizing the main discharge region. However, due to the presence of N.sub.2 within the discharge region, the aforementioned N.sub.2 --CO.sub.2 ground state pumping effect also occurs resulting in the generation of the parasitic tail pulse.
For some applications, such as a laser range finder, the presence of the parasitic tail pulse not only decreases the power of the main pulse but may also mask returns from relatively nearby targets. Thus, the strong suppression or the total elimination of the parasitic pulse is a desirable goal in such applications.
Previously known methods of reducing the parasitic tail pulse include providing a Q-switch or removing the N.sub.2 altogether from the laser. The installation of a Q-switch is disadvantageous in that it adds additional cost and complexity to the laser. The removal of N.sub.2 from the laser is also disadvantageous in that the UV radiation supplied by the N.sub.2 is an important element of the preionization.